1. Field of the Invention
The present invention generally relates to a laminated impedance device, and more particularly, to a laminated impedance device including a variety of electronic circuits that define a noise filter.
2. Description of the Related Art
A laminated impedance device of this type as disclosed in Japanese Unexamined Patent Application Publication No. 9-7835 or Japanese Utility Model Laid-Open No. 6-82822 is well known in the art. Such a laminated impedance device includes a laminate formed by laminating a plurality of coil units having different permeabilities. The coil units are associated with coil conductor patterns which are electrically connected to each other in series to define a spiral coil. The laminated impedance device ensures high impedance in a wide frequency range from a low frequency to a high frequency, thereby extending the noise-free frequency band.
In the prior art laminated impedance device, a first external electrode is connected to the coil conductor patterns in a high-permeability coil unit, while a second external electrode is connected to the coil conductor patterns in a low-permeability coil unit. Thus, a problem occurs in that the electrical properties of the impedance device differs depending upon which one of the high-permeability coil unit and the low-permeability coil unit is used as a mounting surface when mounted on a printed board.
To overcome the above-described problems, preferred embodiments of the present invention provide a laminated impedance device which can be mounted on any surface without altering the electrical properties thereof.
To this end, a laminated impedance device according to a preferred embodiment of the present invention includes a high-permeability coil unit having a laminate of a plurality of magnetic layers made of a relatively-high-permeability material and a plurality of coil patterns, the high-permeability coil unit including at least first and fourth coil portions, and a low-permeability coil unit including a laminate of a plurality of magnetic layers made of a relatively-low-permeability material and a plurality of coil patterns, the low-permeability coil unit including at least second and third coil portions. The high-permeability coil unit and the low-permeability coil unit are stacked on each other such that the first coil portion, the second coil portion, the third coil portion, and the fourth coil portion are electrically connected in series in a sequential manner to define a spiral coil. The laminated impedance device according to this preferred embodiment may be a laminated inductor.
The first and fourth coil portions of the high-permeability coil unit are connected to input and output external electrodes so as to ensure consistent electrical properties regardless of the mounting direction or orientation.
The second coil portion and the third coil portion of the low-permeability coil unit are preferably wound such that a magnetic flux generated by the second coil portion is directed in a different direction from a magnetic flux generated by the third coil portion. This provides electromagnetic coupling of the magnetic flux generated by the second coil portion and the magnetic flux generated by the third coil portion, thereby yielding a high inductance in the low-permeability coil unit.
The first coil portion and the fourth coil portion of the high-permeability coil unit are wound such that a magnetic flux generated by the first coil portion is in the same direction as a magnetic flux generated by the fourth coil portion. Therefore, an electromagnetic coupling of the magnetic flux generated by the first coil portion and the magnetic flux generated by the fourth coil portion does not occur. This prevents a high-frequency component input to the laminated impedance device from directly flowing to the output side due to the electromagnetic coupling of the first and fourth coil portions of the high-permeability coil unit, thereby avoiding the phenomenon where the high-frequency component is not passed to the second and third coil portions of the low-permeability coil unit.
The first, second, third, and fourth coil portions are wound such that a magnetic flux generated by the first coil portion of the high-permeability coil unit is directed in a different direction from a magnetic flux generated by the second coil portion of the low-permeability coil unit and a magnetic flux generated by the fourth coil portion of the high-permeability coil unit is directed in a different direction from a magnetic flux generated by the third coil portion of the low-permeability coil unit. Therefore, an electromagnetic coupling of the magnetic flux generated by the high-permeability coil unit and the magnetic flux generated by the low-permeability coil unit does not occur. This allows the impedance characteristic of the high-permeability coil unit to operate independently from the impedance characteristic of the low-permeability coil unit. As a result, the high-permeability coil unit effectively removes low-frequency noise, while the low-permeability coil unit effectively removes high-frequency noise.